243 research outputs found
Recalling Obaid
I sit here at the assisted living facility where I am well cared for, searching for memories of my first meeting with Obaid Siddiqi. It must have been 1961. I had known about Obaid for some time, since he had done his thesis work with my friend and colleague Guido Pontecorvo
On-chip interference of single photons from an embedded quantum dot and an external laser
In this work, we demonstrate the on-chip two-photon interference between
single photons emitted by a single self-assembled InGaAs quantum dot and an
external laser. The quantum dot is embedded within one arm of an air-clad
directional coupler which acts as a beam-splitter for incoming light. Photons
originating from an attenuated external laser are coupled to the second arm of
the beam-splitter and then combined with the quantum dot photons, giving rise
to two-photon quantum interference between dissimilar sources. We verify the
occurrence of on-chip Hong-Ou-Mandel interference by cross-correlating the
optical signal from the separate output ports of the directional coupler. This
experimental approach allows us to use classical light source (laser) to assess
in a single step the overall device performance in the quantum regime and probe
quantum dot photon indistinguishability on application realistic time scales.Comment: 5 pages, 3 figure
Photon Statistics of Filtered Resonance Fluorescence
Spectral filtering of resonance fluorescence is widely employed to improve
single photon purity and indistinguishability by removing unwanted backgrounds.
For filter bandwidths approaching the emitter linewidth, complex behaviour is
predicted due to preferential transmission of components with differing photon
statistics. We probe this regime using a Purcell-enhanced quantum dot in both
weak and strong excitation limits, finding excellent agreement with an extended
sensor theory model. By changing only the filter width, the photon statistics
can be transformed between antibunched, bunched, or Poissonian. Our results
verify that strong antibunching and a sub-natural linewidth cannot
simultaneously be observed, providing new insight into the nature of coherent
scattering.Comment: Main manuscript 7 pages with 4 figures, supplementary material of 4
page
Observation of large spontaneous emission rate enhancement of quantum dots in a broken-symmetry slow-light waveguide
Quantum states of light and matter can be manipulated on the nanoscale to
provide a technological resource for aiding the implementation of scalable
photonic quantum technologies [1-3]. Experimental progress relies on the
quality and efficiency of the coupling between photons and internal states of
quantum emitters [4-6]. Here we demonstrate a nanophotonic waveguide platform
with embedded quantum dots (QDs) that enables both Purcell-enhanced emission
and strong chiral coupling. The design uses slow-light effects in a glide-plane
photonic crystal waveguide with QD tuning to match the emission frequency to
the slow-light region. Simulations were used to map the chirality and Purcell
enhancement depending on the position of a dipole emitter relative to the air
holes. The highest Purcell factors and chirality occur in separate regions, but
there is still a significant area where high values of both can be obtained.
Based on this, we first demonstrate a record large radiative decay rate of 17
ns^-1 (60 ps lifetime) corresponding to a 20 fold Purcell enhancement. This was
achieved by electric-field tuning of the QD to the slow-light region and
quasi-resonant phonon-sideband excitation. We then demonstrate a 5 fold Purcell
enhancement for a dot with high degree of chiral coupling to waveguide modes,
substantially surpassing all previous measurements. Together these demonstrate
the excellent prospects for using QDs in scalable implementations of on-chip
spin-photonics relying on chiral quantum optics.Comment: 15 pages, 4 figures, 1 table. Supporting information is available
upon request to the corresponding autho
Interfacing a quantum dot spin with a photonic circuit
A scalable optical quantum information processor is likely to be a waveguide
circuit with integrated sources, detectors, and either deterministic
quantum-logic or quantum memory elements. With microsecond coherence times,
ultrafast coherent control, and lifetime-limited transitions, semiconductor
quantum-dot spins are a natural choice for the static qubits. However their
integration with flying photonic qubits requires an on-chip spin-photon
interface, which presents a fundamental problem: the spin-state is measured and
controlled via circularly-polarised photons, but waveguides support only linear
polarisation. We demonstrate here a solution based on two orthogonal photonic
nanowires, in which the spin-state is mapped to a path-encoded photon, thus
providing a blue-print for a scalable spin-photon network. Furthermore, for
some devices we observe that the circular polarisation state is directly mapped
to orthogonal nanowires. This result, which is physically surprising for a
non-chiral structure, is shown to be related to the nano-positioning of the
quantum-dot with respect to the photonic circuit
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